PERFORMANCE OF PRESSURIZED ANODE SUPPORTED SOLID OXIDE FUEL CELL

Nathanael Royer, Ryan Hamilton, Jeffrey Collins,

John Drazin, Dustin McLarty

Outline

• Motivation for Pressurization

• The De-coupled Hybrid Cycle

• WSU’s Test Stand

• Initial Test Results

• Upgraded Stack Results

Why Pressurization?

• Increased performance– Higher Nernst potential– Reduced activation losses and gas diffusion

• Efficient hybridization

• Reduced steam methanation kinetics distributes reforming across cell

• Compact gas manifolding

• Possibility of pressure sealing– Vessel pressure applies external force

evenly to seal area

• Hydrogen production at storage/use pressure

De-coupled Hybrid

• 65 kW gas turbine + 400kW SOFC @ 70% LHV

• Oxygen membrane isolates SOFC from gas turbine– Separate startup– Increased operating range

• Pure oxygen cathode should improve performance

Test Station Design

• Furnace rating: 10 bar, 1000 °C

• Bronkhorst mas flow meters with 50:1 turndown ratio:

• Anode: 5slpm N2, 5slpm H2, 0.2 slpm CO2, 2 slpm CO, and 5slpm CH4

• Cathode: 10slpm N2 and 10slpm O2

• Independent/coupled back pressure control to 145 psi for cathode/anode/furnace

• A hydraulic ram assembly to provide stack compression for sealing.

Stack Design

• Copper cored electrodes for high current, >50 amps

• Separate alumina spinel coated Inconel preheaters for anode and cathode gases.

• Concentric piping, inlet inside exhaust, reduces furnace penetrations and improves pre-heating

Stack Sealing

• Kerafol glass seal cell to tray

• Flexitallic’s Thermiculite 866 seals tray to interconnect and interconnect to manifold.

• Compressed to 10 MPa with external press

Flow Plate Design

• Cross flow interconnect plates:

• Channels:1 mm wide, 1mm deep at 1mm spacing

• Thermally sprayed with manganese cobalt spinel

Cell Specs and Procedures

• Elcogen anode supported cell with an active area of 9 cm X 9 cm.

• NiO/YSZ anode, 8YSZ electrolyte, and an LSC cathode with a GDC diffusion barrier layer.

• Silver and nickel mesh were used as current collectors at the cathode and anode respectively.

Start Up Procedures• Warm up at at 2 °C per min to 750 ° C

• Dwell at 500 °C for glass binder burnout

• Cathode flow: 0.2 SLPM of O2 and 0.8 SLPM N2

• Anode flow: 1 SLPM N2 was initiated

• Cell reduction at 750 °C: procedure below

• Conditioning: constant current density of 0.25 A cm2

Step Time

(min)

Anode (slpm) Cathode (slpm)

H2 N2 O2 N2

Reduction 1 60 0.1 2.5 0.2 0.8

Reduction 2 30 0.1 1.5 0.2 0.8

Reduction 3 30 0.2 1 0.2 0.8

Conditioning 30 0.5 0.5 0.2 0.8

Leak Characterization• Measured OCV at atmospheric

flow was lower than the theoretical voltage by 87 mV, indicating an internal gas leak.

• Leakage is likely due to a cracked cell or glass seal.

• Predicted OCV and the measured OCV began to converge with increasing applied pressure.

• Higher pressure decreases average gas velocity, minimizing leakage.

I-V cell characterization• Despite the leakage, the cell

was functioning, and I-V curves were collected.

• By increasing pressure from atmospheric to 9 bar, the power density at 0.85 V saw a 37.3% increase.

• ASR was not constant, varying from 1.01 Ω cm2 at atmospheric pressure then dropping to 0.76 Ω cm2 at 3 bar, and again increasing to 0.82 Ω cm2 at 9 bar.

Impact of Pressurization on Performance

• Changing from baseline conditions to pressurized operation (6 bar), with a 100% oxygen cathode resulted in a 61% improvement in operating power at a voltage of 0.85V

• There is a decrease in performance between 6 bar and 10 bar.

Oxygen Concentration Sweep

Atmospheric Pressure 3 bar Gauge

• Testing was performed at a constant 50% H2 utilization, and 12.5 % O2 utilization.

• Improvement exceeds that expected from enhanced Nernst Potential

• Pressurization is significantly reducing loss mechanisms above 3bar

Impact of Pressurization on Performance

Current Degradation With Time

• Significant degradation, which slowed slightly after 200 hrs.

• Chrome volatilization suspected

Direct Internal Methane Reforming

• The fuel inlet gas composition was 0.3 slpm H2, 0.1 slpm N2, 0.45 slpm H2O, and 0.15 slpm CH4, for a total anode flow rate of 1 slpm.

• A brief period without steam after atmospheric testing significantly degraded cell performance.

• Pressurization may be key to unlocking SOFC potential

• WSU has developed new testing capabilities

• Demonstrated 61% performance improvement

• Degradation needs further investigation

• Complete direct internal reforming is possible at pressure

• This work is made possible with support from the ARPA-E

Integrate program award DE-AR0000960

Conclusions